Method for depositing tin oxide and titanium oxide coatings on flat glass and the resulting coated glass

ABSTRACT

A chemical vapor deposition process for laying down a tin or titanium oxide coating on a glass substrate through the use of an organic oxygen-containing compound and the corresponding metal tetrachloride. The organic oxygen compound is preferably an ester having an alkyl group with a β hydrogen in order to obtain a high deposition rate. The resulting article has a tin or titanium oxide coating which can be of substantial thickness because of the high deposition rates attainable with the novel process, and, in the case of titanium oxide coating possesses a desirable refractive index greater than 2.4. The coating growth rates resulting from the method of the present invention may be at least 130 Å per second.

RELATED APPLICATION

This application is a continuation of application Ser. No. 08/696,203filed Aug. 13, 1996, which is hereby incorporated by reference. Thisapplication is claiming the benefit under 35 U.S.C. §120 of saidapplication Ser. No. 08/696,203 filed under 35 U.S.C. §111.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for depositing titanium oxide andtin oxide coatings on a flat glass substrate, and the resulting coatedglass. More particularly, this invention relates to a chemical vapourdeposition process for producing titanium oxide and tin oxide coatingson flat glass using a coating precursor gas mixture comprising thecorresponding metal tetrachloride and an organic oxidant.

2. Summary of Related Art

Titanium oxide and tin oxide coatings have been proposed for use onglass containers, for example bottles, to improve the mechanicalstrength of the containers. It has also been proposed to use bothtitanium oxide and tin oxide coatings on flat glass to modify thecharacteristics of the glass for architectural use; titanium oxidecoatings deposited under vacuum (by reactive sputtering) are used ascomponents of sputtered multi-layer infrared reflecting coatings, whiletin oxide coatings are used, not only as layers of multi-layer sputteredcoatings, but also deposited pyrolytically with a dopant as infraredreflecting and/or electroconducting coatings.

GB patent specification 1,115,342 describes a process for producingglass containers with good inherent strength and good abrasionresistance by spraying the containers, while still hot from themanufacturing process, with a solution or dispersion of stannic chloride(that is, tin tetrachloride) in an organic liquid, isopropyl alcoholbeing preferred. A small amount of titanium chloride may be incorporatedas a modifier. The liquid solution is fed to atomisers, which may be ofthe pressure jet variety, located on either side of a tunnel over aconveyor for hot glass bottles to produce a ‘mist of liquid reagent’ sothat a layer of liquid is formed on all the external surfaces of thebottles where it reacts to form a layer of tin oxide.

GB patent specification 1,187,784 describes an improvement of theprocess described in GB patent specification 1,115,342 and apparentlymore suitable for incorporation into a process for the automaticmanufacture of glassware without interfering with the normal running ofsuch process and without requiring additional supervision. Thespecification proposes to treat glass containers, at high temperature,with a liquid solution of an organic compound of tin “which compound hasproperties such that upon application of heat it decomposes into twomaterials, one of which is an organic compound of tin of highdecomposition temperature which reacts with the glass surface to producea diffusion layer of tin oxide within the glass surface, while the otheris a volatile compound of tin such that a substantial proportion ofvapour of said compound is produced, and subjecting the containers to aheat treatment such that a reaction is caused to occur between the glassat least the surfaces of the containers and the tin compounds”. Thematerial used for treating the glass containers may be provided byreacting tin tetrachloride with organic substances containing carbonylgroups of moderate activity e.g. organic esters of ethyl, n-propyl,isopropyl, n-butyl and isobutyl alcohols with acetic, propionic andbutyric acids. The resulting solution may be sprayed, in the presence ofambient atmosphere, on to the hot containers e.g. in the form of a finemist after they leave the forming machine and before they enter theannealing lehr. GB patent specification 1 187 783 describes an analogousprocess to that described in 1 187 784 in which an organic compound oftitanium is sprayed on to the hot glass containers in place of theorganic compound of tin. The organic titanium compound may be produced,in an analogous manner to the organic compound of tin, by reactingtitanium tetrachloride with an organic ester e.g. n-butyl acetate.Again, the resulting solution is sprayed onto the glass in the ambientatmosphere on the container production line.

It has also been proposed to use tin tetrachloride, applied either as aliquid spray or, more recently, in gaseous form, to apply a tin oxidecoating to hot flat glass to form an electroconductive, infra-redreflecting coating on the hot glass surface; water is used to hydrolysethe tin tetrachloride and as a source of oxygen for formation of the tinoxide.

Processes involving use of the reactants in gaseous form (also calledCVD or chemical vapour deposition processes) have certain advantagesover spray processes for coating flat glass, especially when thereactants can be premixed before application to the glass.Unfortunately, tin tetrachloride reacts readily with water so thatprevious proposals to use tin tetrachloride and water vapour in gaseousform have usually involved supplying the gases separately to the glasssurface and mixing them while in contact with the glass.

GB patent specification 2 044 137A relates to such a process in whichdiscrete laminar streams of each reactant are formed and projected on toa hot glass substrate by bringing the streams together in reciprocaltangential contact over the glass. Titanium tetrachloride may be used asone of the gaseous reactants, in place of the tin tetrachloride, inorder to form a titanium oxide coating. The patent also suggestssupplying hydrogen to one of the gas streams to attenuate the violentreaction between the tin tetrachloride and the water vapour. This may bedone either by direct addition of gaseous hydrogen, or by the additionof methanol, which is said to react in situ to produce the desiredgaseous hydrogen.

GB patent specification 2 026 454B describes a process in which acoating chamber is positioned over a hot float glass ribbon as itadvances from the float bath and successive gaseous streams of (1)preheated nitrogen carrier gas, (2) tin tetrachloride entrained inpreheated nitrogen and (3) air, water vapour and hydrofluoric acid areintroduced into the coating chamber so they flow along the glasssubstrate surface being coated as a substantially turbulence free layer.The patent specifies the concentration of water vapour and tintetrachloride in the gaseous medium over the glass.

European patent specifications 0 365 239B1 and 0 376 240B1 describe amethod and apparatus for depositing a tin oxide coating on a hot glassribbon. A first gaseous stream of tin tetrachloride in preheated dry airis caused to flow along the surface of the hot ribbon of glass advancingbeneath a coating chamber, a second turbulent stream of hydrofluoricacid and steam introduced into the coating chambers at right angles tothe plane of the glass and direction of flow of the first gaseousstream, and the combined first and second gas streams drawn through thecoating chamber over the glass under turbulent flow conditions. Themethod and apparatus may also be used to apply a coating of titaniumoxide using titanium tetrachloride in place of the tin tetrachloride.

U.S. Pat. No. 4,590,096 describes a process in which a coating solutioncomprising a substantially solvent free mixture of an organotin chlorideand a reactive organic fluorine compound soluble in or miscible with theorganotin chloride is introduced to a preheated carrier gas stream whichcontains sufficient water vapour that the relative humidity of the gasstream at 18° C. is about 6% to about 100%. The resulting gas stream ispassed over a hot glass surface to deposit a fluorine doped tin oxidecoating on the hot glass. A wide range of organotin compounds may beused, and the possibility of using tin tetrachloride is mentioned.Similarly, a wide range of organic fluorine compounds, including oxygencontaining compounds, for example trifluoroacetic acid andethyltrifluoroacetate, may be used. Some of the fluorine-containingdopants have limited solubilities in the organotin compounds used, andan optional solubiliser may be used to increase the solubility of thefluorine dopant on the organotin compound; acetic anhydride, ethylacetate, hexane, methyl isobutyl ketone and butyraldehyde are listed asnon-limiting examples of the solubilisers that may be used. However, theU.S. patent, in common with the other patents utilising chemical vapourdeposition methods to deposit a metal oxide from a gaseous metaltetrachloride, utilises water vapour as the source of oxygen.

U.S. Pat. No. 4,751,149 Vijaykumar et al is concerned with deposition ofzinc oxide coatings by chemical vapour deposition at low temperature(60° to 350° C., preferably 100° to 200° C.) on heat sensitivephotoconductor substrates, and proposes to deposit the zinc oxidecoatings from an organozinc compound and an oxidant, which may be anoxygen containing organic compound e.g. an ester, and an inert carriergas. Although the patent is not entirely clear, it apparently proposesto introduce separate streams of the organozinc compound and oxidantinto the deposition chamber, and certainly there is no proposal topre-mix these components together before delivery to the coatingchamber.

It would be advantageous to provide a method for depositing tin ortitanium oxide coatings by a CVD process applied to hot flat glass usinga premixture of the corresponding metal tetrachloride as a low costreactant and a source of oxygen without premature reaction between themetal tetrachloride and oxygen source (previously water) resulting information of metal oxide in the coating equipment with consequentproblems and inefficiency. It would be particularly advantageous if themethod allowed for deposition of the coating at high rates.

It is an object of the present invention to provide a method forobtaining tin and titanium oxide coatings on a substrate at highdeposition rates. High deposition rates are important when coatingsubstrates in a manufacturing process. This is particularly true for anon-line float glass process where the glass ribbon is traveling at aspecific line speed and where the ribbon requires a specific coatingthickness. The deposition rates obtained with the preferred embodimentsof the present invention may be ten times higher than the depositionrates with other known methods for depositing titanium oxide coatings.Especially high deposition rates, particularly for titanium oxide, maybe achieved with the present invention using a precursor mixtureincluding an ester with a β hydrogen.

Another object of the present invention is to provide a method forobtaining a tin oxide or titanium oxide coating wherein the thickness ofthe coating can be varied based upon the particular organic compoundutilized as a source of oxygen in the precursor mixture.

A further object is to obtain a titanium oxide coating at highdeposition rates with a refractive index of at least 2.4.

A still further object is to produce tin and titanium oxide coatings athigh deposition rates using low cost chlorinated precursors.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a chemicalvapour deposition process for laying down a tin oxide or titanium oxidecoating on a hot glass substrate using a precursor gas mixturecontaining the corresponding metal tetrachloride and an organic sourceof oxygen, without the requirement for inclusion of water vapour and theconsequent risk of premature reaction.

The present invention provides a process for depositing a tin oxide ortitanium oxide coating on hot flat glass comprising the steps of

-   -   (a) preparing a precursor gas mixture containing the        corresponding metal tetrachloride and an organic oxygen        containing compound as a source of oxygen for formation of the        metal oxide,    -   (b) maintaining said precursor gas mixture at a temperature        below the temperature at which the metal tetrachloride reacts to        form the metal oxide while delivering the mixture to a coating        chamber opening on to the hot glass,    -   (c) introducing the precursor gas mixture into the coating        chamber whereby the mixture is heated to cause deposition of the        corresponding metal oxide incorporating oxygen from the organic        compound on to the hot glass surface.

Surprisingly, a wide range of oxygen-containing organic compounds may beused as the source of oxygen, without requiring the presence of watervapour or gaseous oxygen, including compounds normally consideredreducing agents rather than oxidising agents, for example, alcohols.However, the preferred organic compounds are carbonyl compounds,especially esters; and particularly good results have been obtainedusing esters having an alkyl group with a β hydrogen. The alkyl groupwith a β hydrogen will normally contain two to ten carbon atoms.

It is preferred to use organic compounds, especially esters, containingfrom two to ten carbon atoms, since larger molecules tend to be lessvolatile and hence less convenient for use in the CVD process of thepresent invention.

Particularly preferred esters for use in the practice of the presentinvention include ethyl formate, ethyl acetate, ethyl propionate,isopropyl formate, isopropyl acetate, n-butyl acetate and t-butylacetate.

The method of the present invention is generally practiced in connectionwith the formation of a continuous glass ribbon substrate, for exampleduring a float glass production process. However, the method of thepresent invention may be employed in coating other flat glass substrateseither on-line or off-line.

The present invention involves the preparation of a precursor gasmixture which includes tin or titanium tetrachloride and an organicoxygen containing compound; a carrier gas or diluent, for example,nitrogen, air or helium, will normally also be included in the gasmixture. Since thermal decomposition of the organic oxygen containingcompound may initiate the metal oxide deposition reaction at a highrate, it is desirable that the precursor mixture be kept at atemperature below the thermal decomposition temperature of the organicoxygen compound to prevent prereaction of the gaseous mixture withformation of the metal oxide.

The gaseous mixture is maintained at a temperature below that at whichit reacts to form the metal oxide, and delivered to a location near aflat glass substrate to be coated, the substrate being at a temperatureabove said reaction temperature (and above the decomposition temperatureof the organic oxygen compound in the precursor gas mixture).

The precursor gas mixture is thereafter introduced into the vapor spacedirectly over the substrate. The heat from the substrate raises thetemperature of the precursor gas above the thermal decompositiontemperature of the organic oxygen compound. The organic oxygen compoundthen decomposes with reaction with the metal tetrachloride producing ametal dioxide coating on the substrate.

The present invention permits the production of tin and titanium oxidecoatings deposited on the hot glass at a high deposition rate e.g. over130 Å/second and, in preferred embodiments, over 250 Å per second.

The deposition rate is dependent upon the particular organic oxygencontaining compound used, and the concentrations of both the organicoxygen containing compound and the metal chloride, as well as thetemperature of the glass. For any particular combination of compounds,the optimum concentrations (and in particular the optimum proportion oforganic oxygen containing compound to metal tetrachloride) and flowrates for rapid coating deposition may be determined by simple trial.However, it will be appreciated that the use of higher concentrations ofreactants and high gas flow rates is likely to result in a lessefficient overall conversion of the reactants into coating, so that theoptimum condition for commercial operation may differ from theconditions which provide the highest deposition rates.

The method of the invention permits the production, at high rates, oftitanium oxide and tin oxide coatings on hot flat glass substrates online during the glass production process. The titanium oxide coatingsmay be produced with a high refractive index (at least 2.4) permittingthe achievement of desired optical effects, especially when used incombination with other coating layers. The tin oxide coatings may bedoped, for example with fluorine, increasing their electricalconductivity and infra red reflectivity, and hence their utility aselectrical conducting coatings and/or low emissivity coatings inarchitectural glazing and other applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other advantages of the present invention, willbecome readily apparent to those skilled in the art from the followingdetailed description of preferred embodiments when considered in thelight of the accompanying drawings in which:

FIG. 1 is a schematic view of a vertical section of an apparatus forpracticing a float glass process which includes gas distributorssuitably positioned to enable the practicing of the method of thepresent invention.

FIG. 2 is broken sectional view of an article coated according to thisinvention; and

FIG. 3 is an enlarged schematic end view of a gas distributor beamsuitable for use in practicing the present invention.

FIG. 4 is an enlarged schematic end view of an alternative gasdistributor beam which may be used in practicing the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, there is illustratedgenerally at 10 in FIG. 1 a float glass installation utilized as a meansfor practicing the method of the present invention. The float glassapparatus more particularly comprises a canal section 12 along whichmolten glass 14 is delivered from a melting furnace (not shown), to afloat bath section 16 wherein a continuous glass ribbon 18 is formed inaccordance with the well known float process. The glass ribbon 18advances from the bath section 16 through an adjacent annealing lehr 20and a cooling section 22. The continuous glass ribbon 18 serves as thesubstrate upon which the metal oxide coating is deposited in accordancewith the present invention.

The float section 16 includes a bottom section 24 within which a bath ofmolten tin 26 is contained, a roof 28, opposite sidewalls 30, and endwalls 32. The roof 28, side walls 30, and end walls 32 together definean enclosure 34 in which a non-oxidizing atmosphere is maintained toprevent oxidation of the molten tin.

Additionally, gas distributor beams 64, 66 and 68 are located in thebath section 16. The gas distributor beams 64 and 66 in the bath sectionmay be employed to apply additional coatings onto the substrate prior toapplying the tin or titanium oxide coating by the method of the presentinvention. The additional coatings may include silicon and silica.

In operation, the molten glass 14 flows along the canal 36 beneath aregulating tweel 38 and downwardly onto the surface of the tin bath 26in controlled amounts. On the tin bath the molten glass spreadslaterally under the influences of gravity and surface tension, as wellas certain mechanical influences, and it is advanced across the bath toform the ribbon 18. The ribbon is removed over lift out rolls 40 and isthereafter conveyed through the annealing lehr 20 and the coolingsection 22 on aligned rolls 42. The application of the coating of thepresent invention may take place in the float bath section 16, orfurther along the production line, for example in the gap between thefloat bath and the annealing lehr, or in the annealing lehr.

A suitable non-oxidizing atmosphere, generally nitrogen or a mixture ofnitrogen and hydrogen in which nitrogen predominates, is maintained inthe bath enclosure 34 to prevent oxidation of the tin bath. Theatmosphere gas is admitted through conduits 44 operably coupled to adistribution manifold 46. The non-oxidizing gas is introduced at a ratesufficient to compensate for normal losses and maintain a slightpositive pressure, on the order of about 0.001 to about 0.01 atmosphereabove ambient atmospheric pressure, so as to prevent infiltration ofoutside atmosphere. Heat for maintaining the desired temperature regimein the tin bath 26 and the enclosure 34 is provided by radiant heaters48 within the enclosure. The atmosphere within the lehr 20 is typicallyatmospheric air, while the cooling section 22 is not enclosed and theglass ribbon is open to the ambient atmosphere. Ambient air may bedirected against the glass ribbon as by fans 50 in the cooling section.Heaters (not shown) may also be provided within the annealing lehr forcausing the temperature of the glass ribbon to be gradually reduced inaccordance with a predetermined regime as it is conveyed therethrough.

FIG. 1 illustrates the use of gas distributor beams 64, 66 and 68positioned in the float bath 16 to deposit the various coatings on theglass ribbon substrate. The gas distributor beam is one form of reactorthat can be employed in practicing the process of the present invention.

A conventional configuration for the distributor beams suitable forsupplying the precursor materials in accordance with the invention isshown generally schematically at FIG. 3. An inverted generallychannel-shaped framework 70 formed by spaced inner and outer walls 72and 74 defines enclosed cavities 76 and 78. A suitable heat exchangemedium is circulated through the enclosed cavities 76, 78 in order tomaintain the distributor beams at a desired temperature.

The precursor gas mixture is supplied through a fluid cooled supplyconduit 80. The supply conduit 80 extends along the distributor beam andadmits the gas through drop lines 82 spaced along the supply conduit.The supply conduit 80 leads to a delivery chamber 84 within a header 86carried by the framework. Precursor gases admitted through the droplines 82 are discharged from the delivery chamber 84 through apassageway 88 toward a coating chamber defining a vapour space openingon to the glass where they flow along the surface of the glass 18 in thedirection of the arrows in FIG. 3.

Baffle plates 90 may be provided within the delivery chamber 84 forequalizing the flow of precursor materials across the distributor beamto assure that the materials are discharged against the glass 18 in asmooth, laminar, uniform flow entirely across the distributor beam.Spent precursor materials are collected and removed through exhaustchambers 92 along the sides of the distributor beam.

Various forms of distributor beams used for chemical vapour depositionare suitable for the present method and are known in the prior art.

One such an alternative distributor beam configuration is illustratedschematically in FIG. 4 of the drawings. Using this distributor, whichis generally designated 100 (and more fully described in European patentEP 0 305 102B), the precursor gas mixture is introduced through a gassupply duct 101 where it is cooled by cooling fluid circulated throughducts 102 and 103. Gas supply duct 101 opens through an elongatedaperture 104 into a gas flow restrictor 105.

Gas flow restrictor 105 is of the kind more fully described in UK patentspecifications GB 1 507 996, and comprises a plurality of metal stripslongitudinally crimped in the form of a sine wave and vertically mountedin abutting relationship with one another extending along the length ofthe distributor. Adjacent crimped metal strips are arranged “out ofphase” to define a plurality of vertical channels between them. Thesevertical channels are of small cross-sectional area relative to thecross-sectional area of gas supply duct 101, so that the gas is releasedfrom the gas flow restrictor 105 at substantially constant pressurealong the length of the distributor.

The coating gas is released from the gas flow restrictor into the inletside 107 of a substantially U-shaped guide channel generally designated106 comprising inlet leg 107, coating chamber 108 which opens onto thehot glass substrate 110 to be coated, and exhaust leg 109, whereby usedcoating gas is withdrawn from the glass. The rounded corners of theblocks defining the coating channel promote a uniform laminar flow ofcoating parallel to the glass surface across the glass surface to becoated.

The following examples (in which gas volumes are expressed understandard conditions, i.e. one atmosphere pressure and ambienttemperature, unless other stated) which constitute the best modepresently contemplated by the inventor for practicing the invention, arepresented solely for the purpose of further illustrating and disclosingthe present invention, and are not to be construed as a limitation on,the invention:

EXAMPLES 1 TO 5

In this series of Examples, a bi-directional coating reactor of the typeshown in FIG. 3 was employed in the laboratory to deposit a titaniumoxide coating.

In Examples 1, 2 and 3, the glass was heated on a conveyor furnace tosimulate the coating reaction conditions of a float glass process inorder to test the method of the present invention. The furnace utilizedin-line rollers to convey a glass substrate through a heating zone priorto practicing the method of the present invention. In Example 1, theglass substrate was float glass which had been initially provided with asilica coating. The silica coating was deposited on the float glassthrough a known chemical vapour deposition process utilizing a precursorof monosilane in an oxygen enriched atmosphere. The silica depositionforms no part of the present invention.

In accordance with the present invention, a titanium oxide coating wasdeposited on the silica coated substrate. The substrate was at atemperature of a 1170° F./630° C. and the substrate line speed was at300 inches/8 metres per minute.

To deposit the titanium oxide, a precursor gas mixture was developedcomprising titanium tetrachloride, ethyl acetate, oxygen, and helium.Helium was included in the precursor mixture as a carrier for thereactants. The precursor mixture was prepared by simultaneouslyintroducing all four gas streams through a manifold system. An in linestatic mixer was used to ensure a homogeneous precursor mixture. Thevolume percent composition of the precursor mixture was 0.7% titaniumtetrachloride, 17.2% ethyl acetate, 7.2% oxygen, and 74.9% helium, withthe flow rates for the components at the manifold being as shown in theaccompanying Table 1.

The temperature of the precursor mixture was kept above 300° F./150° C.in order to prevent the adduct reaction of titanium tetrachloride andethyl acetate. The precursor temperature was also kept below the 950°F.-1130° F. (510° C.-610° C.) thermal decomposition temperature range ofethyl acetate in order to prevent the mixture from prereacting.

The precursor mixture was introduced into the reactor just above themoving substrate. The temperature at the precursor tower was 250°F./120° C. The temperature at the reactor face was 350° F./175° C. Thehigher substrate temperature initiated the thermal decomposition of theethyl acetate which then resulted in the deposition of the titaniumoxide.

The resulting coated glass was allowed to cool in air and the coatinganalysed. It was found to be titanium oxide with a carbon content of2.5-3.5 atomic percent. The thickness of the titanium oxide coating wasmeasured 490 Å and the thickness and growth rate (150 Å per second) areshown in Table 1. The optical properties of the resulting productincluded an observed Illuminant C transmittance (10° observer) of 62.3%and an observed Illuminant C reflectivity of 35.6%. The extinctioncoefficient was 0.008 at 550 nm, and the refractive index of thetitanium oxide coating was 2.44.

In Examples 2 and 3 the coating procedure set out in Example 1 wasrepeated, except that in Example 2 ethyl formate was used as the organicsource of oxygen, and in Example 3 isopropanol was used as the organicsource of oxygen and uncoated glass (in place of the silicon oxidecoated glass of Examples 1 and 2) was used as the substrate. The gasflow rates used and, in the case of Example 2, the thickness and growthrate of the titanium oxide coating produced are shown in Table 1. InExample 3, the isopropanol burned in the reactor leaving onlyparticulate titanium oxide on the glass, the corresponding depositionrate therefore being quoted as 0 Å/second.

The procedure for Examples 4 and 5 was as used in the previous Examples(the reactor temperature and the substrate being identical to Example1), except that the substrate was static and not dynamic. The staticsample was positioned under the reactor for 10 seconds. Under staticconditions, the residence time of the substrate under the reactor isincreased from the dynamic conditions by a factor of five.

In Example 4, methyl acetate was used as the organic source of oxygen,and in Example 5 t-butyl acetate was used; in each case a titanium oxidecoating was produced. The gas flow rates, resulting titanium oxidecoating thickness and coating growth rates are as shown in Table 1. Therelatively slow growth rate achieved using methyl acetate is discussedhereinafter. TABLE 1 Flow rates (litres/minute) Organic Growth Exam-Titanium oxygen Oxy- He- Thick-

te ple tetrachloride compound gen lium ness Å Å/s

1 0.2 4.8 ethyl 2.0 20.9 490 150 acetate 2 0.5 1.6 ethyl 6.0 17.4 800250 formate 3 0.45 1.5 isopropanol 4.0 15.45 0 0 4 0.5 1.2 methyl 6.017.4 <100 <10 formate 5 0.5 0.5 t-butyl 6.0 16.5 1300 130 acetate

EXAMPLE 6

A float glass process was used in producing a continuous glass ribbonhaving a thickness of 0.125 inches/3 mm at a line speed of 434 inches/11metres per minute. The glass temperature was at 1140° F./615° C. at thedesired point of application in the float bath section of a titaniumoxide coating using a coating reactor similar to that shown in FIG. 3.The temperature at the precursor tower was 400° F./205° C. and thetemperature at the reactor face was 500° F./260° C. Prior to practicingthe method of the present invention, a silica coating was deposited onthe glass substrate in the float bath section at a thickness of about339 Å. The same chemical vapor deposition process as described inExample 1 was used to deposit the silica coating. The silica depositionforms no part of the present invention.

The precursor gas mixture was developed comprising titaniumtetrachloride and ethyl acetate in a helium carrier gas. Oxygen was notused in the precursor as result of earlier Examples indicated that thecoating reaction was not sensitive to the oxygen concentration. Theprecursor mixture was prepared by simultaneously introducing the threecomponents through a manifold system. The volume percent composition ofthe precursor mixture was 0.6% titanium tetrachloride, 1.8% ethylacetate, and 97.5% helium. The flow rates for the components were 480.0l/m of helium, 3.0 l/m of titanium tetrachloride, 9.2. l/m of ethylacetate. The total flow rate for the precursor mixture was 492.2 l/m.

The resulting titanium oxide coating was 684 Å thick. The carbon contentof the coating was less than 2 atomic percent. The growth rate of thecoating was 309 Å per second.

EXAMPLE 7

The same procedure carried out Example 6 was utilized in this Example.The substrate comprised coatings of silicon and then silica over theglass substrate. The coatings were deposited by a known chemical vapordeposition process in the float bath section. The silicon coating wasdeposited by CVD from monosilane with a non-oxidizing carrier gas. Thesilica coating was then deposited onto the silicon coating through theuse of the same procedure as described in Example 1.

The precursor for the titanium oxide coating included titaniumtetrachloride and ethyl acetate in a helium carrier gas. The volumepercent composition of the precursor was 0.5% titanium tetrachloride,1.9% ethyl acetate, and 97.6% helium. The corresponding flow rates forthe components were 480.0 l/m of helium, 2.4 l/m of titaniumtetrachloride, 9.2 l/m of ethyl acetate. The total flow rate for theprecursor mixture was 491.6 1/m.

The resulting coated article 52 is illustrated in FIG. 2. The glasssubstrate 54 is depicted with a stack of multiple coatings 56. Thecoatings comprise a layer of silicon 58, a layer of silica 60, then atitanium oxide coating 62 on top of the article. The titanium oxidecoating on the resulting article had a thickness of 836 Å. The opticalproperties of the resulting coating stack included an observedIlluminant C transmittance of 13.1% and an observed Illuminant Creflectivity of 82.5%. The growth rate of the titanium oxide coating was378 Å per second.

EXAMPLES 8-13

In this series of Examples, a static coater was used in the laboratoryto apply a tin oxide coating on to a float glass substrate carrying acolour suppressing silicon oxide layer produced as described in Europeanpatent EP 0 275 662B.

The float glass to be coated was supported on a nickel block in areactor vessel and the block heated from below by electric heatingelements to provide a glass temperature of 1085° F./585° C. A flatgraphite plate was mounted approximately 0.4 inches/10 mm above theglass and parallel thereto to provide a gas flow path 0.4 inches/10 mmdeep between the glass surface bearing the silicon oxide layer and theplate.

A precursor gas mixture containing tin tetrachloride and an organicsource of oxygen, in air and a small proportion of additional nitrogenas carrier gas, was delivered through a gas line maintained at atemperature of 435° F.±25° F./225° C.±15° C. and provided with a fishtail nozzle opening on to the gas flow path over the hot glass in ageneral direction parallel to the glass surface. The total carrier gasflow rate was 13 m³/hour. The flow rates of the tin tetrachloride, andthe nature and flow rates of the organic compound used, were as shown inthe accompanying Table 2. In Examples 9 and 11, small amounts of 40%hydrogen fluoride were incorporated in the-precursor gas mixture to dopethe resulting tin oxide coating with fluorine, as shown in the Table.

The gas flow containing the reactant gases was applied for approximately8 seconds, and the coating apparatus and coated glass then allowed tocool under a flow of air at 345° F./225° C. On dismantling the coatingapparatus, the delivery gas line, nozzle and plate defining the gas flowpath over the glass found to be free, in each case, from deposit,indicating an absence of undesirable prereaction. In each case, theglass had a tin oxide coating applied over the silicon oxide, thethickness of the coating varying with distance from the fishtail nozzle.The maximum thickness and corresponding growth rate for each precursorgas mixture used is shown in Table 2. The emissivity, resistivity andhaze of the samples producing using hydrogen fluoride to incorporate afluorine dopant (Examples 9 and 11) were measured and the resultsreported in Table 2.

This series of Examples shows that an organic source of oxygen can beused as part of a premixed precursor gas mixture comprising tintetrachloride to deposit a tin oxide coating without significantundesirable prereaction detrimentally affecting the coating process e.g.by deposition of tin oxide in the gas supply ducts. Moreover, ifdesired, a source of dopant, such as hydrogen fluoride, may beincorporated in the gaseous premixture to reduce the emissivity andresistivity of the coating while continuing to avoid significantdetrimental prereaction. TABLE 2 Precursor Gas Mixture Organic OxygenSource SnCl₄ Flow 40% HF Max tin Max growth Flow Rate Rate Flow Rateoxide rate Resistivity Example (ml/min) Compound (ml/min) (ml/min)thickness Å Å/second Emissivity ohm/cm Haze 8 12 ethyl acetate 10 — 2750344 — — — 9 12 ethyl acetate 10 1 2680 335 0.25 5.3 × 10⁻⁴ 0.4% 10 12butyl acetate 13.4 — 3460 432 — — — 11 12 butyl acetate 13.4 1.3 2880360 0.25 6.9 × 10⁻⁴ 0.6% 12 6 isopropyl 120 — 2284 262 — — — alcohol 1317 trifluoracetic 16.2 — 2840 335 — — — acid

EXAMPLE 14

In this Example, a coating distributor as illustrated schematically inFIG. 4 was used in a float bath to apply a coating of tin oxide by amethod in accordance with the invention. The ribbon speed wasapproximately 233 inches per minute/350 minutes per hour and the glassthickness was 0.05 inches/1.2 mm. The glass temperature wasapproximately 1170° F./630° C. The temperature of the gas supply duct101 which served as a primary gas mixing chamber was maintained at 300°F./150° C. and the ‘static’ waffle gas distributor 105 was approximately645° F./340° C. The tin tetrachloride and butyl acetate vapors weredelivered by bubbling nitrogen through the liquids maintained at 175°F./80° C. in bubblers and, hence, through separate heated conduits togas supply duct 101. The vapors mixed at the primary chamber, passedthrough the waffle pack gas distributor, and then under laminar flowconditions through U-shaped guide channel 106 comprising coating chamber108 opening on to the hot glass ribbon.

The flow rates used were sufficient to obtain tin tetrachloride:butylacetate molar ratios of between 1:1 and 1:5. The trial was carried outfor 5 hours. On dismantling the coater it was discovered that the cooledsurfaces and the associated conduits were over 90% free of deposits,thus showing that tin tetrachloride and butyl acetate used for producinga tin dioxide coating on glass can be premixed with one another withoutsubstantial prereaction. A thin tin oxide coating was obtained on theglass ribbon.

It will be appreciated that various changes and modifications can bemade from the specific details of the invention as incorporated in theforegoing Examples without departing from the spirit and scope thereofas defined in the appended claims.

In its essential details, the invention is a continuous chemical vapordeposition process for laying down tin oxide and titanium oxide coatingsonto a glass substrate at high deposition rates through the use of thecorresponding metal tetrachloride and an organic compound used as asource of oxygen in a preformed precursor gas mixture.

The metal tetrachlorides are preferred sources of the respective metalsbecause of the availability and cost of the raw material.

It has been found, especially when depositing titanium oxide coatingsfrom titanium tetrachloride, that, in order to form the metal oxide atthe optimum deposition rates, it is desirable to use an organic oxygencontaining compound which is an ester, particularly an ester in whichthe group derived from the alcohol is an alkyl group with a β hydrogen.Additionally, the decomposition temperature of the ester should not begreater than the reaction temperature of the coating precursor gasmixture at the desired point of application. Esters utilized in theprecursor gas mixture that have a β hydrogen and appropriatedecomposition temperatures will deposit the coatings at high depositionrates. The preferred group of esters used in practicing the presentinvention includes the group consisting of ethyl formate, ethyl acetate,ethyl propionate, isopropyl formate, isopropyl acetate, n-butyl acetate,and t-butyl acetate.

In general an ester decomposes in a continuous fashion over a giventemperature range. In the present invention, the thermal decompositiontemperature of the ester is defined as the temperature at which theunimolecular decomposition rate constant of the ester is 0.01/sec. Theunimolecular decomposition rate constants of common esters such as ethylacetate and t-butyl acetate are well known and can be found in thechemical literature. For ethyl acetate and t-butyl acetate, the thermaldecomposition temperatures using the above definition are 935 and 650°Fahrenheit (500° C. and 344° C.), respectively. One skilled in the artwill recognize that the choice of ester and specific depositiontemperature employed will determine the optimum coating growth rate.Reaction temperatures below the defined thermal decompositiontemperature, but within the decomposition range of the selected ester,will result in lower coating growth rates.

In accordance with the present invention, the alkyl group of an esterused in the coating precursor gas mixture may be a carbon compoundhaving a range of 2-10 carbon atoms. The lower limit of the range isdictated by the β hydrogen requirement on the alkyl group. The upperlimit is to avoid flammability and volatility issues that arise when thealkyl group contains more than ten carbon atoms.

In practicing the method of the present invention, a manifold may beused to connect and regulate the individual gas streams to formulate thecoating precursor gas mixture. A common delivery line may be used todeliver the precursor gas mixture from the manifold to the gas beamdistributor. An in line static mixer may be used in the delivery line toensure a homogeneous gas mixture. Additionally, the baffles in the gasdistributor beam, illustrated in FIG. 3, or a gas flow restrictor asdescribed with reference to FIG. 4, may provide further mixing of theprecursor gas at the reactor stage.

In many of the Examples, oxygen was included in the coating precursorgas mixture. However, the deposition rate of the metal oxide coating wasnot sensitive to the oxygen concentrations, and no oxygen gas was usedin Examples 6 or 7 showing the inclusion of oxygen to be unnecessary.

The concentration of the reactive components of the coating precursorgas mixture may be selected to obtain the optimum coating growth rate.The concentration of metal tetrachloride is generally 0.1 to 5.0 percentby volume in the precursor gas mixture. The concentration of metaltetrachloride is based upon the amount of metal needed to provide thedesired coating thickness in the available residence time. Thus themetal tetrachloride concentration is adjusted according to processvariables, such as the line speed of the ribbon in a float glassprocess.

The concentration of the organic oxygen compound in the coatingprecursor gas mixture is generally one to five times the concentrationof the metal tetrachloride, being selected within this range based uponthe deposition temperature. When using an ester, lower depositiontemperatures will result in slower ester decomposition rates andtherefore, will require greater concentrations of the ester to reactwith the metal tetrachloride. In Examples 6 and 7, the optimumconcentration of the ethyl. acetate in the precursor gas mixture is 1 to3 times the concentration of the titanium tetrachloride. Concentrationsabove or below the optimum range will produce metal oxide coatings atlower coating growth rates.

The temperature of the precursor gas mixture is critical for control ofthe reaction, in particular to avoid undesirable pre-reaction or adductformation resulting in formation of an involatile product in theprecursor lines. In one preferred embodiment, especially applicable whenusing an ester, the temperature is maintained above 300° F./150° C. inthe precursor gas lines. The precursor gas mixture is also preferablykept below the thermal decomposition temperature of the organic oxygen.compound to prevent prereaction of the mixture.

The present inventive process utilizes the heat from the substrate toinitialize the coating reaction. In on-line situations, such as thefloat glass process, the substrate is formed at extremely hightemperatures. Therefore, the method of the present invention may beapplied at a point in the float glass process where the substratetemperature is lowered but is still above the temperature at which thecoating is formed (and preferably after the glass ribbon hassubstantially finished stretching i.e. below 1380° F./750° C.). Off-lineapplications of the present invention will require heating the substrateto a temperature above the decomposition temperature of the ester.

In practicing the method of the present invention in the float glassprocess, the preferred point of application is in the float bathsection. The temperature range at the point of application for thecoating is usually about 1100°-1320° F./590°-715° C. The temperature isan important operating parameter because it influences the concentrationof the organic compound utilized in the precursor gas mixture. Thetemperatures of the substrate in the float bath section are relativelystable and therefore exhibit little variation at the point ofapplication. In examples 6 and 7 using ethyl acetate, the preferredsubstrate temperature range is 1100°-1250° F./590° C.-680° C.

The heat from the substrate raises the temperature of the precursor gasmixture above the temperature required for coating formation (and whenan ester is used as the organic compound above thermal decompositiontemperature of the ester). The metal deposition reaction may beinitiated by the decomposition of the organic oxygen compound. Whentitanium tetrachloride is used in combination with an ester having analkyl group with a β hydrogen, the titanium oxide coating then forms onthe substrate at decomposition rates that are ten times higher thanknown coating methods. In the on-line application with a float glassribbon process, the ribbon passes under the gas distributor beam at arelatively fast rate. The metal oxide coating is deposited onto thefloat glass ribbon as the ribbon passes under the coater.

The inventors propose the following theory regarding the chemicalreaction that may take place when using an ester having an alkyl groupwith a β hydrogen. However, the inventors do not wish to limit theinvention to just this possible explanation, and therefore offer itmerely as an aid to understanding the results of the present inventiveprocess.

The inventors propose that as the ester decomposes, the carbon-hydrogenbond on one of the β hydrogens breaks and the hydrogen transfers to thecarbonyl group eliminating an alkene and forming a caboxylic acid. Thehydrolysis reaction simultaneously takes place between the carboxylicacid and the metal tetrachloride leading to the formation of the metaloxide coating on the substrate.

In general, the resulting article produced in accordance with thepresent invention comprises a substrate having a titanium oxide or tinoxide coating. The coating may be applied directly to the substrate oras a layer in a plurality of coatings on a substrate. The rate ofdeposition of the metal oxide coating is effected by the decompositionrate of the organic oxygen compound. At constant reaction temperaturesdifferent organic oxygen compounds will provide different coating growthrates because of the difference in the decomposition temperatures.Therefore, the desired metal oxide coating growth rate for a givensystem is selected by matching a specific organic oxygen compound to theprecursor gas mixture temperature and the substrate temperature at thepoint of application.

The deposition rate of the titanium oxide coating in the presentinvention may be ten times greater than rates in known depositionmethods. The present inventive process permits deposition rates over 130Å per second with some deposition rates measured well over 300 Å persecond. The higher deposition rates for titanium oxide yield a coatingwith a refractive index greater than 2.4.

In the present invention, the resulting oxide coating contains littleresidual carbon from the decomposition of the organic oxygen compound,especially when an ester is used. Carbon is an undesirable by product ofthe coating reaction because high levels of carbon in depositioncoatings create absorption problems with the coating. The concern inusing an organic oxygen compound in the coating precursor gas mixture isthat decomposition will result in levels of carbon that adversely affectthe absorption properties of the finished glass. The carbon content inthe coatings produced from the method of the present invention showedless than four atomic percent of carbon where measured. This low levelof carbon will not significantly affect absorption properties of thecoating.

It is to be understood that the forms of the invention herewith shownand described are to be taken as illustrative embodiments only of thesame, and that various changes in the shape, size and arrangement ofparts, as well as various procedural changes, may be resorted to withoutdeparting from the spirit of the invention.

1-32. (canceled)
 33. A titanium dioxide photocatalyst structurecomprising: a transparent glass substrate having first and secondopposing surfaces, said transparent glass substrate containing alkalineingredients therein, the first surface of said substrate receiving lightfrom an external light source; a titanium dioxide film having first andsecond opposing surfaces, a light transmittance of said titanium dioxidefilm being at least 50% for light having a wavelength of 550 nm, thefirst surface of said titanium dioxide film being formed on the secondsurface of said substrate, whereby light transmitted from said externalsource through the first and second opposing surfaces of said substrateand through the first surface of said titanium dioxide film to thesecond surface thereof causes photocatalytic activity to be generated onthe second surface of said titanium dioxide film; and a transparentprecoat film interposed between the second surface of said substrate andthe first surface of said titanium dioxide film.
 34. The titaniumdioxide photocatalyst structure according to claim 33, wherein saidtransparent precoat film has a thickness of 0.02 μm to 0.2 μm.
 35. Thetitanium dioxide photocatalyst structure according to claim 34, whereinsaid precoat film is composed of SiO₂.
 36. A titanium dioxidephotocatalyst structure comprising: a transparent substrate; a titaniumdioxide film formed on said substrate, said titanium dioxide film havingphotocatalytic activity and a light transmittance of at least 50% forlight having a wavelength of 550 nm; and a transparent precoat filmdisposed between the transparent substrate and the titanium dioxidefilm.
 37. The titanium dioxide photocatalyst structure according toclaim 36, wherein the precoat film has a thickness of 0.02 μm to 0.2 μm.38. The titanium dioxide photocatalyst structure according to claim 36,wherein the precoat film is composed of SiO₂.
 39. A method for producinga titanium dioxide photocatalyst structure according to claim 36comprising a producing process which includes the step of forming thetitanium dioxide film on the transparent substrate by a method selectedfrom the group consisting of a pyro-sol method, a dipping method, aprinting method and a CVD method.
 40. A titanium dioxide photocatalyststructure comprising: a transparent substrate; a titanium dioxide filmformed on said substrate, said titanium dioxide film having a thicknessof 0.1 μm to 5 μm, photocatalytic activity and a light transmittance ofat least 50% for light having a wavelength of 550 nm; and a transparentprecoat film disposed between the transparent substrate and the titaniumdioxide film.
 41. The titanium dioxide photocatalyst structure accordingto claim 40, wherein the precoat film has a thickness of 0.02 μm to 0.2μm.
 42. The titanium dioxide photocatalyst structure according to claim40, wherein the precoat film is composed of SiO₂.
 43. A titanium dioxidephotocatalyst structure comprising: a transparent substrate; a titaniumdioxide film, containing an anatase crystal, formed on said substrate,said titanium dioxide film having photocatalytic activity and a lighttransmittance of at least 50% for light having a wavelength of 550 nm;and a transparent precoat film disposed between the transparentsubstrate and the titanium dioxide film.
 44. The titanium dioxidephotocatalyst structure according to claim 43, wherein the precoat filmhas a thickness of 0.02 μm to 0.2 μm.
 45. The titanium dioxidephotocatalyst structure according to claim 43, wherein the precoat filmis composed of SiO₂.